Perceptual and Moior Shills, 1976,43, 115-120. @ Perceptual and Motor Skills 1976
ARE TWO HANDS BETTER THAN ONE? ASSESSING PJFORMATION ACQUIRED FROM ONE- AND TWO-HANDED HAPTIC EXPLORATION OF RANDOM FORMS ELIOT J. BUTTER AND DAVID F. BJORKLUND University o f Dayton Summary.-15 male undergraduates were presented with 10-sided random forms which they explored visually, or one-handed haptically, or two-handed haptically. Forms were exposed for various durations and subjects were required to draw each form immediately after its removal. The results indicated that 30 sec of one-handed exploration and 20 and 30 sec of two-handed exploration produced performance comparable to just 2 sec. of visual exploration. Twohanded exploration was significantly superior to one-handed exploration only at the 20-sec. exposure duration. These results illustrate the disparity in the information-gathering capabilities between the visual and haptic systems.
Studies investigating the relative efficacy of shape matching in adults between vision and touch have found that visual examination yields significantly more accurate performance than haptic exploration ( Abravanel, 1971, 1973; Cashdan 8: Zung, 1970; Fico & Brodsky, 1972; Garvill & Molander, 1973; Zung, Butcer, & Cashdan, 1974). It has been suggested that the discrepancy in macching performance between vision and touch may be due to differences in the relative efficiency of each system's ability to gather information and that there may be minimal differences between the modalities in the actual processing of information, e.g., the transforrnacion or retention of information (Bucter & Bjorklund, 1973; Davidson, Abbotc, & Gershenfeld, 1974). Davidson, et al. ( 1974) illustrated that incramodal haptic matching performance was nor statistically differentiated from incramodal visual performance when haptic exposure times were increased from 4 to 16 sec. These authors concluded thac hapcic exploration time is "an apparently important determinant of accuracy matching within touch and across touch and vision" (p. 542). In an attempt to compare the relative amount of information result~ng from controlled visual and haptic exposures to similar stimuli, Butter and Bjorklund ( 1973) manipulated exposure times to random forms and required subjects to reproduce (draw) the forms after eicher visual or haptic exploration. Butter and Bjorklund reported that 30 sec. of one-handed haptic exploration was required before performance was comparable to just 2 sec. of visual exploration. It was suggested that the substantial disparity in the information-gathering capacities of vision and touch might be decreased if forms were bimanually exp!ored. The present research employs a methodology similar to thac of Butter and Bjorklund ( 1973) in investigating the efficacy of bimanual haptic exploration of random forms relative to unimanual haptic and visual exploration. Will
116
E. J. BUTTER
&
D. F. BJORKLUND
two-handed haptic exploration result in the acquisition of more "usable" information or will the extra hand merely get in the way and add a confusion factor to an already complicated task? In order to evaluate the information-gathering capabilities of bimanual haptic search relative to unimanual haptic and visual exploration, college students were required to reproduce random forms after various exposures. It was anticipared that bimanual haptic exploration would result in superior performance relative to unimanual haptic search, and chat, relative to one-handed haptic exploration, a shorter exposure period would be required before bimanual haptic performance was comparable to performance at brief visual exposures.
METHOD Subjects
Fifteen male undergraduate students from a medium-sized, private midwestern university served as subjects.
Design Subjects were presented with 50 10-sided random forms which they explored visually, one-handed haptically, and two-handed haptically. Visual exposures were for 2 and 5 sec., while haptic exposures (both uni- and bimanual) were for 5, 10, 20, and 30 sec. This resulted in 10 modaliry X exposure conditions, e.g., visual 2-sec.; unimanual haptic 5-sec., etc. Because of the large between-subject variability in drawing skills, a within-subject design was employed, with subjects receiving five trials under each of the 10 conditions. Trials were divided into five blocks, with 10 trials per block, and with a form for each condition being presenced once per block. A single random assignment of forms was determined, with all subjects receiving the same 50 forms in the same presentation order. Each form was presenced only once.
Stimuli and Appa~atzu The 10-sided random forms, construcced following Lobb ( 1965), were cut from %-in. masonite. They varied in size and area but were never larger than 14 un. (distance between two most extreme points) nor shorter than 6 un. Although several of the angles were slight, all forms were sufficiently large so that all angles were judged to be haptically discriminable. A small square peg mas mounted on the back of each form which enabled it to be placed in a square hole in a 9- by 18-un wooden formboard, tilted at a 40' angle. The form was raised approximately 3 cm above the formboard to afford the subject adequate manipulation of the form. Each subject was seated in front of a box-like structure, which measured approximately 90 by 56 cm. Across the bottom front of che structure was a 20-un aperture covered by a black curtain to prevent subjects from seeing any form during a haptic trial. Exposure times were measured by a manual stop watch controlled by the experimenter.
HAPTIC EXPLORATION OF RANDOM FORMS
The procedure used was similar to that employed by Butter and Bjorklund ( 1973). Each subject was seated in front of the apparatus and given paper and
a pencil. Instructions were read by a male experimenter. Subjects were told that they would be presented with 50 10-sided random forms which they were to draw after exploring the forms visually, with one hand, or with two hands. Subjects were informed of the modality and exposure condition at the beginning of each trial. On visual trials the experimenter placed the formboard and form in front of the subject. For haptic presentations the subject put his hand(s) under the curtain and felt the form in the formboard. Each subject was instructed to draw the 10-sided form the best he could immediately after it was removed from him. Two scorers, blind to the exposure and modality condition, rated each drawing for accuracy of match to the 10-sided random forms. A scale from 0 to 10 was used, corresponding to the number of approximate correct lines and angles drawn by subject. Discrepancies between raters were discussed and a single score was mutually agreed upon for each drawing. Butter and Bjorklund (1973) report a reliability coefficient of .93 between two raters scoring a similar task.
RESULTS Subjects' drawings were rated for accuracy of match to the standard forms. Accuracy scores ranged from zero ( n o congruence between the drawing and the form) to 10 (all lines and angles of the form accurately represented in the drawing). The number of lines drawn per form ranged from 6 to 17, with a mean of 9.98 and a mode of 10. Although the subjects were told that all forms were 10-sided, only 36% of the 750 drawings had exactly 10 sides; however, the distribution of the number of sides to a drawing was approximately normal, with 69% of all drawings having between 9 and 11 sides. On the average then, the subjects seemed to maximize their chance of obtaining points for their drawings by including approximately 10 sides in the majority of their figures. Further, the number of sides included in each drawing did not appear to vary systematically over modality and exposure conditions. The mean accuracy scores for the five drawings per subject for each condition were calculated and averaged across subjects (see Fig. 1). As can be seen from Fig. 1 visual performance at 2-sec. exposure appears comparable to onehanded haptic exposure at 30 sec. and two-handed haptic exposures at 20 and 30 sec. A one-way analysis of variance with repeated measures computed on the accuracy scores for the 10 modality X exposure times conditions confirmed this impression. The analysis was significant ( F G , 1 2 " = 18.87, p < .001) with Duncan's multiple-range test indicating that performance associated with 2 sec. of visual exposure being comparable to 30 sec. of one-handed haptic exploration and 20 and 30 sec. of two-handed haptic search. All other haptic conditions
E. J. BUTTER & D. F. BJORKLUND
-
VISUAL
-
0 -ONE HAND HAPTIC x TWO-HAND n m T l c
-
I 1
2
I 5
I PO
I
10
I 30
EXPOSURE TIME
FIG.1. Mean accuracy scores for the three treatment groups as a function of exposure time (sec.)
(all 5- and 10-sec. exposures and the 20-sec. one-handed condition) resulted in significantly poorer performance relative to 20 sec. of visual inspection. The 5-set. visual condition was best over-all and was statistically superior to other conditions except the 20- and 30-sec. bimanual exposures. Differences between these two haptic conditions and the 5-sec. visual condition did, however, approach statistical significance ( p < . l o ) with 5-se~.visual condition showing slightly greater performance. A further examination of Fig. 1 illustrates that two-handed haptic exploration produced consistently higher performance than one-handed haptic search, but with the exception of the 20-sec. exposure, the differences were small. In general, haptic performance increased with increasing exposure times. Only between the 20- and 30-sec. bimanual exposures is this trend not seen. A 4 (exposure times) )( 2 (number of hands) analysis of variance with repeated measures on both factors performed on the haptic data only confirmed the trends apparent in Fig. 1. Both the main effects of exposure times (F3,4? = 25.25, p < .01) and number of hands ( F l V l 4= 11.05, p < .01) were significant, as was the interaction of exposure times X number of hands (P3.45 = 3.64, p < .05). Duncan's multiple-range test performed on the exposure time factor for the uni- and bimanual haptic conditions showed that accuracy scores increased with increasing exposure times except between the 20- and 30-sec. two-handed exposures. Further, although two-handed search was over-all superior to onehanded exploration, Duncan's multiple-range test comparing performance between one- and two-handed exploration at each exposure time illustrated that only at the 20-sec. exposures was the difference between one and two hands statistically reliable. At the other exposure times (5, 10, and 30 sec.) twohanded inspection was not statistically differentiated from unimanual exploration, although the direction of the difference was always in favor of bimanual exploration. The results concerning unimanual haptic and visual exploration of random
HAPTIC EXPLORATION OF RANDOM FORMS
119
forms replicate the earlier findings of Butter and Bjorklund ( 1973). Thirty seconds of one-handed haptic exploration resulted in performance comparable to when forms were visually inspected for only 2 sec. In the present study onehanded haptic exploration of less than 30 sec. consistently resulted in poorer performance than 2 sec. of visual inspection. Two-handed haptic exploration resulted in over-all improved performance relative to unimanual haptic search. However, only at the 20-sec. exposures was bimanual exploration statistically greater than one-handed inspection. Apparently, for relatively brief exposures, e.g., 5 and 10 sec., two-handed haptic search yields no more usable information than does one-handed exploration. This may be due to a confusion effect. The two hands may not be making an organized search at such short exposures. It appears that only for longer exposures do the two hands become coordinated and thus able to gather more information than in a unimanual search. It is not known whether longer haptic exposures would have resulted in still further improvements in subjects' accuracy scores or whether a performance ceiling for haptic exploration has been attained here. The lack of performance difference between 20 and 30 sec. of two-handed search suggests that, for bimanual haptic exploration, asymptotic performance may have been realized. That this is not the absolute limit of task performance has been noted by Butter and Bjorklund ( 1973). These authors reported appreciably superior reproduction scores to those reported here when subjects visually inspected random forms for 15 sec. in a very similar task (mean accuracy score = 7.91 out of a possible 1 0 ) . One reason for the large performance differences between haptic and visual exploration seems apparent. When vision is used, all aspects of a small stimulus, as was employed in this study, are simultaneously available for inspection. Haptic exploration, however, demands serial processing. Such processing, where information must be integrated over time, may severely limit the absolute level of performance which can be attained from a haptic search. Similarly, a subject's memory may be overly taxed when the haptic mode is used. Areas of a form which are searched early may be forgotten by the time the later sections are inspected. Each form must be constantly reinspected in an attempt to relearn sections of the figure which have since been forgotten as other areas of the stimulus are examined. Perhaps only by overlearning the dimensions of a stimulus can all relevant aspects of a form be held in memory long enough to accurately reproduce the form. If this is the case, our data indicate that the time necessary for this overlearning would likely be prohibitive when complex, planometric stimuli are used. An alternative explanation relates to the novelty of the situation. Subjects have not developed well-defined haptic search strategies which they can use efficiently to gain information from handling the random forms. Perhaps what is needed is nor longer exposure times, per se, but merely more exposures so that subjects can develop strategies or rules to guide their haptic search behavior.
E J. BUTTER
120
&
D. F. BJORKLUND
The limitation may not be in the modality as much as it is in the search strategies (or lack of them) that a subject brings to the task. Unfortunately, our data does not adequately direct itself to this question. In summary, it appears that, for the most part, two hands are only slightly better than one. At very short exposures, e.g., 5 and 10 sec., and for extended exposures, e.g., 30 sec., one-handed haptic exploration is only slightly less effective than two-handed inspection in acquiring shape information. Evidently, birnanual exploration does facilitate performance when exposures are between 10 and 20 sec. Additionally, these results further illustrate the disparity in the information-gathering capabilities between the visual and haptic modalities. Whether the discrepancies between these systems are primarily related to the inherent information-processing characteristics of these two modalities (simultaneous vs serial) or differences in the employment of appropriate search strategies, can not be discerned from this research. REFERENCES ABRAVANEL, E Active detection of solid-shape information by touch and vision. Perception and Psychophysics, 1971, 10, 358-360.
ABRAVANEL,E. Retention of shape information under haptic or visual acquisition. .Perceptual and Motor Skills, 1973, 36, 683-689.
BUTTER,E. J., & BJORKLUND, D. F. Investigating information-gathering capabilities of visual and haptic modalities. Perceptual and Motor Skills, 1973, 37, 787-793.
CASHDAN, S., & ZUNG,B. The effect of sensory modality and delay on form recognition.
journal o f Experimental Psychology, 1970, 86, 458-460. & GERSHENFBLD, J. Influence of exploration time on haptic and visual matching of complex shape. Perception and Psychophysics, 1974, 15, 539-543. FICO, J. M., & BRODSKY, H. S. The effect of visual and tactual stimulation on learning of abstract forms. Psychononzic Science, 1972, 27, 246-248. GARVILL, J., & MOLANDER, B. Effects of standard modality, comparison modality, and retention interval on matching of form. Scandinmian Journal o f Psychology, 1973, 14, 203-206. LOBB,H. Vision versus touch in form discrimination. Canadian Journal o f Psychology, 1965.. 19.. 175-187. ZUNG,B. J., BUmm, E. J., & CASHDAN, S. Visual-haptic form recognition with task delay and sequenced bimodal input. Neuropsychologia, 1974, 12, 73-81.
DAVmSON, P. W., ABBOTT, S.,
Accepted May 14, 1976.
ARE TWO HANDS BETTER THAN ONE? ASSESSING PJFORMATION ACQUIRED FROM ONE- AND TWO-HANDED HAPTIC EXPLORATION OF RANDOM FORMS ELIOT J. BUTTER AND DAVID F. BJORKLUND University o f Dayton Summary.-15 male undergraduates were presented with 10-sided random forms which they explored visually, or one-handed haptically, or two-handed haptically. Forms were exposed for various durations and subjects were required to draw each form immediately after its removal. The results indicated that 30 sec of one-handed exploration and 20 and 30 sec of two-handed exploration produced performance comparable to just 2 sec. of visual exploration. Twohanded exploration was significantly superior to one-handed exploration only at the 20-sec. exposure duration. These results illustrate the disparity in the information-gathering capabilities between the visual and haptic systems.
Studies investigating the relative efficacy of shape matching in adults between vision and touch have found that visual examination yields significantly more accurate performance than haptic exploration ( Abravanel, 1971, 1973; Cashdan 8: Zung, 1970; Fico & Brodsky, 1972; Garvill & Molander, 1973; Zung, Butcer, & Cashdan, 1974). It has been suggested that the discrepancy in macching performance between vision and touch may be due to differences in the relative efficiency of each system's ability to gather information and that there may be minimal differences between the modalities in the actual processing of information, e.g., the transforrnacion or retention of information (Bucter & Bjorklund, 1973; Davidson, Abbotc, & Gershenfeld, 1974). Davidson, et al. ( 1974) illustrated that incramodal haptic matching performance was nor statistically differentiated from incramodal visual performance when haptic exposure times were increased from 4 to 16 sec. These authors concluded thac hapcic exploration time is "an apparently important determinant of accuracy matching within touch and across touch and vision" (p. 542). In an attempt to compare the relative amount of information result~ng from controlled visual and haptic exposures to similar stimuli, Butter and Bjorklund ( 1973) manipulated exposure times to random forms and required subjects to reproduce (draw) the forms after eicher visual or haptic exploration. Butter and Bjorklund reported that 30 sec. of one-handed haptic exploration was required before performance was comparable to just 2 sec. of visual exploration. It was suggested that the substantial disparity in the information-gathering capacities of vision and touch might be decreased if forms were bimanually exp!ored. The present research employs a methodology similar to thac of Butter and Bjorklund ( 1973) in investigating the efficacy of bimanual haptic exploration of random forms relative to unimanual haptic and visual exploration. Will
116
E. J. BUTTER
&
D. F. BJORKLUND
two-handed haptic exploration result in the acquisition of more "usable" information or will the extra hand merely get in the way and add a confusion factor to an already complicated task? In order to evaluate the information-gathering capabilities of bimanual haptic search relative to unimanual haptic and visual exploration, college students were required to reproduce random forms after various exposures. It was anticipared that bimanual haptic exploration would result in superior performance relative to unimanual haptic search, and chat, relative to one-handed haptic exploration, a shorter exposure period would be required before bimanual haptic performance was comparable to performance at brief visual exposures.
METHOD Subjects
Fifteen male undergraduate students from a medium-sized, private midwestern university served as subjects.
Design Subjects were presented with 50 10-sided random forms which they explored visually, one-handed haptically, and two-handed haptically. Visual exposures were for 2 and 5 sec., while haptic exposures (both uni- and bimanual) were for 5, 10, 20, and 30 sec. This resulted in 10 modaliry X exposure conditions, e.g., visual 2-sec.; unimanual haptic 5-sec., etc. Because of the large between-subject variability in drawing skills, a within-subject design was employed, with subjects receiving five trials under each of the 10 conditions. Trials were divided into five blocks, with 10 trials per block, and with a form for each condition being presenced once per block. A single random assignment of forms was determined, with all subjects receiving the same 50 forms in the same presentation order. Each form was presenced only once.
Stimuli and Appa~atzu The 10-sided random forms, construcced following Lobb ( 1965), were cut from %-in. masonite. They varied in size and area but were never larger than 14 un. (distance between two most extreme points) nor shorter than 6 un. Although several of the angles were slight, all forms were sufficiently large so that all angles were judged to be haptically discriminable. A small square peg mas mounted on the back of each form which enabled it to be placed in a square hole in a 9- by 18-un wooden formboard, tilted at a 40' angle. The form was raised approximately 3 cm above the formboard to afford the subject adequate manipulation of the form. Each subject was seated in front of a box-like structure, which measured approximately 90 by 56 cm. Across the bottom front of che structure was a 20-un aperture covered by a black curtain to prevent subjects from seeing any form during a haptic trial. Exposure times were measured by a manual stop watch controlled by the experimenter.
HAPTIC EXPLORATION OF RANDOM FORMS
The procedure used was similar to that employed by Butter and Bjorklund ( 1973). Each subject was seated in front of the apparatus and given paper and
a pencil. Instructions were read by a male experimenter. Subjects were told that they would be presented with 50 10-sided random forms which they were to draw after exploring the forms visually, with one hand, or with two hands. Subjects were informed of the modality and exposure condition at the beginning of each trial. On visual trials the experimenter placed the formboard and form in front of the subject. For haptic presentations the subject put his hand(s) under the curtain and felt the form in the formboard. Each subject was instructed to draw the 10-sided form the best he could immediately after it was removed from him. Two scorers, blind to the exposure and modality condition, rated each drawing for accuracy of match to the 10-sided random forms. A scale from 0 to 10 was used, corresponding to the number of approximate correct lines and angles drawn by subject. Discrepancies between raters were discussed and a single score was mutually agreed upon for each drawing. Butter and Bjorklund (1973) report a reliability coefficient of .93 between two raters scoring a similar task.
RESULTS Subjects' drawings were rated for accuracy of match to the standard forms. Accuracy scores ranged from zero ( n o congruence between the drawing and the form) to 10 (all lines and angles of the form accurately represented in the drawing). The number of lines drawn per form ranged from 6 to 17, with a mean of 9.98 and a mode of 10. Although the subjects were told that all forms were 10-sided, only 36% of the 750 drawings had exactly 10 sides; however, the distribution of the number of sides to a drawing was approximately normal, with 69% of all drawings having between 9 and 11 sides. On the average then, the subjects seemed to maximize their chance of obtaining points for their drawings by including approximately 10 sides in the majority of their figures. Further, the number of sides included in each drawing did not appear to vary systematically over modality and exposure conditions. The mean accuracy scores for the five drawings per subject for each condition were calculated and averaged across subjects (see Fig. 1). As can be seen from Fig. 1 visual performance at 2-sec. exposure appears comparable to onehanded haptic exposure at 30 sec. and two-handed haptic exposures at 20 and 30 sec. A one-way analysis of variance with repeated measures computed on the accuracy scores for the 10 modality X exposure times conditions confirmed this impression. The analysis was significant ( F G , 1 2 " = 18.87, p < .001) with Duncan's multiple-range test indicating that performance associated with 2 sec. of visual exposure being comparable to 30 sec. of one-handed haptic exploration and 20 and 30 sec. of two-handed haptic search. All other haptic conditions
E. J. BUTTER & D. F. BJORKLUND
-
VISUAL
-
0 -ONE HAND HAPTIC x TWO-HAND n m T l c
-
I 1
2
I 5
I PO
I
10
I 30
EXPOSURE TIME
FIG.1. Mean accuracy scores for the three treatment groups as a function of exposure time (sec.)
(all 5- and 10-sec. exposures and the 20-sec. one-handed condition) resulted in significantly poorer performance relative to 20 sec. of visual inspection. The 5-set. visual condition was best over-all and was statistically superior to other conditions except the 20- and 30-sec. bimanual exposures. Differences between these two haptic conditions and the 5-sec. visual condition did, however, approach statistical significance ( p < . l o ) with 5-se~.visual condition showing slightly greater performance. A further examination of Fig. 1 illustrates that two-handed haptic exploration produced consistently higher performance than one-handed haptic search, but with the exception of the 20-sec. exposure, the differences were small. In general, haptic performance increased with increasing exposure times. Only between the 20- and 30-sec. bimanual exposures is this trend not seen. A 4 (exposure times) )( 2 (number of hands) analysis of variance with repeated measures on both factors performed on the haptic data only confirmed the trends apparent in Fig. 1. Both the main effects of exposure times (F3,4? = 25.25, p < .01) and number of hands ( F l V l 4= 11.05, p < .01) were significant, as was the interaction of exposure times X number of hands (P3.45 = 3.64, p < .05). Duncan's multiple-range test performed on the exposure time factor for the uni- and bimanual haptic conditions showed that accuracy scores increased with increasing exposure times except between the 20- and 30-sec. two-handed exposures. Further, although two-handed search was over-all superior to onehanded exploration, Duncan's multiple-range test comparing performance between one- and two-handed exploration at each exposure time illustrated that only at the 20-sec. exposures was the difference between one and two hands statistically reliable. At the other exposure times (5, 10, and 30 sec.) twohanded inspection was not statistically differentiated from unimanual exploration, although the direction of the difference was always in favor of bimanual exploration. The results concerning unimanual haptic and visual exploration of random
HAPTIC EXPLORATION OF RANDOM FORMS
119
forms replicate the earlier findings of Butter and Bjorklund ( 1973). Thirty seconds of one-handed haptic exploration resulted in performance comparable to when forms were visually inspected for only 2 sec. In the present study onehanded haptic exploration of less than 30 sec. consistently resulted in poorer performance than 2 sec. of visual inspection. Two-handed haptic exploration resulted in over-all improved performance relative to unimanual haptic search. However, only at the 20-sec. exposures was bimanual exploration statistically greater than one-handed inspection. Apparently, for relatively brief exposures, e.g., 5 and 10 sec., two-handed haptic search yields no more usable information than does one-handed exploration. This may be due to a confusion effect. The two hands may not be making an organized search at such short exposures. It appears that only for longer exposures do the two hands become coordinated and thus able to gather more information than in a unimanual search. It is not known whether longer haptic exposures would have resulted in still further improvements in subjects' accuracy scores or whether a performance ceiling for haptic exploration has been attained here. The lack of performance difference between 20 and 30 sec. of two-handed search suggests that, for bimanual haptic exploration, asymptotic performance may have been realized. That this is not the absolute limit of task performance has been noted by Butter and Bjorklund ( 1973). These authors reported appreciably superior reproduction scores to those reported here when subjects visually inspected random forms for 15 sec. in a very similar task (mean accuracy score = 7.91 out of a possible 1 0 ) . One reason for the large performance differences between haptic and visual exploration seems apparent. When vision is used, all aspects of a small stimulus, as was employed in this study, are simultaneously available for inspection. Haptic exploration, however, demands serial processing. Such processing, where information must be integrated over time, may severely limit the absolute level of performance which can be attained from a haptic search. Similarly, a subject's memory may be overly taxed when the haptic mode is used. Areas of a form which are searched early may be forgotten by the time the later sections are inspected. Each form must be constantly reinspected in an attempt to relearn sections of the figure which have since been forgotten as other areas of the stimulus are examined. Perhaps only by overlearning the dimensions of a stimulus can all relevant aspects of a form be held in memory long enough to accurately reproduce the form. If this is the case, our data indicate that the time necessary for this overlearning would likely be prohibitive when complex, planometric stimuli are used. An alternative explanation relates to the novelty of the situation. Subjects have not developed well-defined haptic search strategies which they can use efficiently to gain information from handling the random forms. Perhaps what is needed is nor longer exposure times, per se, but merely more exposures so that subjects can develop strategies or rules to guide their haptic search behavior.
E J. BUTTER
120
&
D. F. BJORKLUND
The limitation may not be in the modality as much as it is in the search strategies (or lack of them) that a subject brings to the task. Unfortunately, our data does not adequately direct itself to this question. In summary, it appears that, for the most part, two hands are only slightly better than one. At very short exposures, e.g., 5 and 10 sec., and for extended exposures, e.g., 30 sec., one-handed haptic exploration is only slightly less effective than two-handed inspection in acquiring shape information. Evidently, birnanual exploration does facilitate performance when exposures are between 10 and 20 sec. Additionally, these results further illustrate the disparity in the information-gathering capabilities between the visual and haptic modalities. Whether the discrepancies between these systems are primarily related to the inherent information-processing characteristics of these two modalities (simultaneous vs serial) or differences in the employment of appropriate search strategies, can not be discerned from this research. REFERENCES ABRAVANEL, E Active detection of solid-shape information by touch and vision. Perception and Psychophysics, 1971, 10, 358-360.
ABRAVANEL,E. Retention of shape information under haptic or visual acquisition. .Perceptual and Motor Skills, 1973, 36, 683-689.
BUTTER,E. J., & BJORKLUND, D. F. Investigating information-gathering capabilities of visual and haptic modalities. Perceptual and Motor Skills, 1973, 37, 787-793.
CASHDAN, S., & ZUNG,B. The effect of sensory modality and delay on form recognition.
journal o f Experimental Psychology, 1970, 86, 458-460. & GERSHENFBLD, J. Influence of exploration time on haptic and visual matching of complex shape. Perception and Psychophysics, 1974, 15, 539-543. FICO, J. M., & BRODSKY, H. S. The effect of visual and tactual stimulation on learning of abstract forms. Psychononzic Science, 1972, 27, 246-248. GARVILL, J., & MOLANDER, B. Effects of standard modality, comparison modality, and retention interval on matching of form. Scandinmian Journal o f Psychology, 1973, 14, 203-206. LOBB,H. Vision versus touch in form discrimination. Canadian Journal o f Psychology, 1965.. 19.. 175-187. ZUNG,B. J., BUmm, E. J., & CASHDAN, S. Visual-haptic form recognition with task delay and sequenced bimodal input. Neuropsychologia, 1974, 12, 73-81.
DAVmSON, P. W., ABBOTT, S.,
Accepted May 14, 1976.
